1. Field of the Invention
The present invention relates generally to the manufacture of glass articles such as bottles and the like, and more particularly, to methods and apparatus for providing increased productivity in a glass manufacturing process by utilizing a cold blowing gas that is delivered from an insulated manifold, with the cold blowing gas being a mixture of compressed cryogen vapor and ambient air that has been dehumidified, with the injection of the cryogen vapor into the ambient air being performed in stages by utilizing cryogen injectors that are cycled into and out of operation to provide for defrosting and to prevent debilitating accumulations of ice, and with the flows of pressurized cold blowing gas being introduced into mold cavities to hasten the cooling and solidification of newly molded glass articles.
2. Prior Art
In the molding of glass articles such as bottles and the like, a hollow blank or parison of glass is typically formed in a roughing mold, and is inserted into a finishing mold where it is expanded to form an article of desired form. The hollow blank of glass is typically formed by pressing a gob of glass and/or by using a pressurized flow of ambient air as a blowing gas to conform the gob to a desired configuration. The resulting blank roughly approximates the shape of the final article that is to be molded, but has thicker walls and is smaller in size. The blank is expanded in the finishing mold to conform to a desired configuration as defined by the finishing mold. Expansion of the blank is typically effected by pressing and/or by using a pressurized flow of ambient air as a blowing gas.
In the molding of a preliminary article of glass such as a hollow blank or parison, and in the molding of articles of final form such as bottles, it is not uncommon to utilize flows of cooling gas that are directed toward the newly molded articles while the articles are still contained within their mold cavities to speed cooling and solidification of the articles so they can be removed as quickly as possible from their molds. The cooling gas is typically ambient air that has been pressurized by a blower. The cooling gas is typically fed from a manifold through a control valve and ducted into the mold cavities, with the gas having temperatures that lie within a range of about 90 to 100 degrees Fahrenheit, and sometimes higher. Where the articles being molded have been formed using blow-molding techniques, the blowing gas also typically comprises blower-pressurized ambient air that is ducted into the mold cavities at temperatures that lie within a range of about 90 to 100 degrees Fahrenheit, and sometimes higher. In most applications, the flows of cooling gases are uninterrupted extensions of the flows of blowing gases that are delivered into the mold cavities to blow-form articles therein.
In order to further speed the cooling of molded glass articles to diminish their mold retention times, proposals have been made to indirectly cool the articles by providing at least portions of their molds with cooling passages through which a fluid coolant is circulated. However, the degree to which mold cooling can be used to indirectly cool molded glass articles is limited not only by the tendency of this approach to induce defects (the number of defects induced in molded glass articles increases as mold temperatures are diminished), but also by the cost of forming cooling passages in the molds, and by the cost of providing suitable apparatus for maintaining controlled flows of coolant through the cooling passages.
While mold cooling provides some assistance in diminishing mold retention times, the retention times during which newly molded glass articles must be held in their molds to effect proper solidification continue to form "bottlenecks" that obstruct efforts to increase the productivity of existing molding equipment.
3. The Referenced Parent Case
The system of the referenced Parent Case addresses the foregoing and other drawbacks of prior proposals by providing a novel and improved system which utilizes flows of pressurized cold cryogen vapor that are introduced into mold cavities to hasten solidification of glass articles which are being molded therein. In the preferred practice described in the Parent Case, flows of pressurized cold cryogen vapor are used both to cool glass articles that are being molded and to effect blow-molding of the articles. By using cold cryogen vapor in this manner, mold retention times for molded glass articles are significantly reduced, thereby permitting correspondingly significant increases in productivity. As is discussed in the Parent Case, productivity increases of 15 percent and often more are achievable at the relatively low expense that is associated with introducing flows of pressurized cold cryogen vapor into the paths of flow that have traditionally been utilized to duct blowing and/or cooling gases to the mold cavities.
While the Parent Case describes a "most preferred practice" that uses a manifold to deliver compressed air to mold inlets through one system of supply conduits, and that uses a cryogen supply header to deliver cryogen vapor to the mold inlets through a separate set of conduits, difficulties have been encountered in the implementation of this most preferred practice in that the provision of flexible cryogen supply conduits and/or the provision of cryogen supply conduits that have relatively movable components has been found to present a significant challenge which has not been well met by present day technology. Stated in another way, while operable cryogen supply conduits have been made and used in prototype apparatus that embodies the described "most preferred practice," such conduits have been found to not perform in as long-lived and reliable a manner as is desired in a true production environment.
Thus, the practice of the invention of the Parent Case that has been found most practical for present commercial use has been what the Parent Case describes as its "less preferred embodiment," wherein a single set of supply lines is utilized to deliver a cold blowing gas from a manifold to the mold inlets, wherein the cold blowing gas is a mixture of cold cryogen vapor and ambient air. As is explained in the referenced Parent case, a drawback of the practice of this "less preferred embodiment" is that the gas mixture that is supplied to the manifold cannot be much lower in temperature than about 35 degrees Fahrenheit because, if lower temperatures are employed, debilitating buildups of ice will form due to condensation of such water vapor as is present in the ambient air, and these ice buildup will block proper feeding of the gas. As will be apparent, the improvements of the present invention address the problem of these debilitating ice buildups, and provide a system that renders quite attractive the use of what was referred to in the referenced Parent Case as the "less preferred embodiment."
4. The Blow Molding of Glass vs. Plastics Materials
As is explained in the referenced Parent Case, the use of flows of cold cryogen vapor that are introduced into mold cavities is applicable to a variety of glass molding techniques including press molding and blow molding. Cold cryogen vapor introduction can be used in single stage molding procedures as well as in plural-stage molding procedures. In a single stage press-molding procedure, for example, a flow of cold cryogen gas may be introduced into a mold cavity to cool a press-molded article and to cool the plunger that has formed inner surface portions of the article. In a plural stage molding procedure, for example where a hollow blank or parison of glass is first press-formed in a roughing mold, and is then blow-molded in a finishing mold to assume its final form, flows of pressurized cold cryogen vapor may be introduced into the mold cavities in either or both of the roughing and finishing stages to expedite solidification and to permit increased productivity.
However, as was pointed out during the prosecution of the referenced Parent Case, the use of cold blowing gas in the blow molding of glass containers is not analogous to the use of cold blowing gas in conjunction with the blow molding of articles formed from plastics material. Plastics material and glass are such different substances, having such different properties, that it is not at all "obvious" to transfer teachings from the art of plastics blow molding to the art of glass blow molding, or vice versa.
Plastics material and glass "set up," "harden," or "solidify" in very different ways, and have very different sensitivities and reactions to temperature shock. A twelve ounce container formed from plastics material typically weighs about 50 grams. To reduce the temperature of 50 grams of plastics material from a typical blow molding temperature of about 360 degrees Fahrenheit to a typical mold discharge temperature of about 90 degrees Fahrenheit requires the extraction of about 16.3 BTU of heat energy. In contrast, a similarly configured 12 ounce container formed from glass weighs typically about 400 grams. To diminish the temperature of a 12 ounce glass container from a blow molding temperature of about 1,350 degrees Fahrenheit to a typical discharge temperature of about 750 degrees Fahrenheit requires a heat energy release of about 105.6 BTU. Because the thermal conductivities of glass and plastics material (e.g. high density polyethylene) are roughly equal, the much higher heat removal requirement of glass would suggest that the glass container must take more than six times as long to cool sufficiently to open the mold; however, this is not at all the case.
In actual practice, the container that is formed from plastics material actually has about a one-half second longer cooling time than does the glass container, this being due to the vast physical differences between plastics material and glass. Because plastics containers will warp if they are removed from their molds before all portions of the containers' mass have cooled sufficiently, mold retention time for plastics containers must be quite protracted. The long, chain-like molecules that form in the solidification of plastics material during cooling tend to orient themselves differently depending upon the manner in which temperature changes are effected. If one section of a plastics container is "hot" (i.e., insufficiently cooled) when the mold opens, the container will "suck in" or "pucker" as the molecules of plastics material contract during cooling. By keeping the container in the mold, under pressure, during cooling, the plastics container will be forced to retain its shape until all of the necessary heat has been removed.
Glass, on the other hand, has no interlocking chains of molecules. Instead, it has very loosely attracted molecules which actually flow at room temperature. Indeed, glass is technically still a "liquid" at 70 degrees Fahrenheit. The very different characters of plastics material and glass result in very different cooling situations as plastics and glass blow-molded containers are cooled.
While uneven cooling of a glass blow-molded container may create stress points, it does not cause significant warpage. Such stress points as are created in the forming of glass containers are dealt with by passing the containers through a lehr, a long furnace which tempers the glass by reheating it to around 900 degrees Fahrenheit, whereafter the glass is gradually cooled to allow the stress points to relieve themselves. Since the glass containers are put through a lehr, the only cooling that is necessary in conjunction with glass blow molding is a sufficient amount of cooling to assure that molded containers will retain their shape once they have been extracted from the bare molds. Thus an opportunity is presented in the blow molding of glass containers that is not available in the blow molding of forming plastics containers, namely an opportunity to speed up production by discharging newly formed containers from their molds the instant that they become only partially cooled to an extend that they are self supporting and structurally stable.
What the invention of the Parent Case recognizes is that, in the blow molding of hollow glass articles, the only cooling of a newly blow molded glass article that is necessary in order to permit the immediate discharge of the article from its mold is an amount of cooling that is adequate to give the glass enough strength to hold its shape. The invention of the Parent Case addresses this very "minimal need" for cooling in a special way, namely by employing a very fast acting cooling technique that results in creating what essentially amounts to a solidified "skin" on the interior surface of newly formed hollow glass articles. Once this interior "skin" has been cooled sufficiently to act as a stable mainstay that will render the newly molded articles shape-stable, the mold can be opened and the newly molded articles can be removed. The fast formation of an adequately cooled and rigidified interior "skin" permits a newly blow molded glass article to be extracted far more quickly from its mold than previously has been possible with prior glass blow-molding cooling techniques. Thus the molds can be recycled and reused more quickly than has previously been thought to be possible, and a very significant increase in productivity of blow molded articles is achieved while utilizing existing production facilities.